Method for control of an HCCI internal combustion engine in exceptional situations

ABSTRACT

The invention relates to a method defining particular exceptional situations in the operation of an HCCI internal combustion engine, whereby an HCCI operation is either suppressed or enforced.

CROSS REFERENCE TO RELATED APPLICATION

This application is the US National Stage of International ApplicationNo. PCT/DE2003/003455, filed Oct. 17, 2003 and claims the benefitthereof. The International Application claims the benefits of GermanPatent application No. 10258802.3 DE filed Dec. 16, 2002, both of theapplications are incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The present invention relates to a method for controlling the operationof an HCCI internal combustion engine which can be operated in the HCCIoperating mode or in an operating mode using externally applied (spark)ignition and is switched over between said operating modes as a functionof predefined operating parameters.

BACKGROUND OF THE INVENTION

When an internal combustion engine is operated in the HCCI (HomogeneousCharge Compression Ignition) operating mode, which is sometimes alsoreferred to as CAI (Controlled Auto Ignition), ATAC (Active ThermoAtmosphere Combustion) or TS (Toyota Soken), the air-fuel mixture isignited not by externally applied (spark) ignition, but by controlledself-ignition.

The HCCI combustion process can be triggered for example by a highproportion of hot residual exhaust gases and/or by a high compressionand/or a high inlet air temperature. A prerequisite for theself-ignition is a sufficiently high energy level in the cylinder.Internal combustion engines which can be operated in the HCCI operatingmode, which engines may be spark ignition engines or diesel engines, areknown; see, for example, U.S. Pat. Nos. 6,260,520, 6,390,054, DE 199 27479 and WO 98/10179.

Compared with a conventional combustion process based on externallyapplied (spark) ignition, HCCI combustion has the advantage of reducedfuel consumption and lower exhaust emissions. The internal combustionengine is therefore operated largely in the HCCI operating mode.However, in certain operating ranges such as, for example, at highengine speeds or under heavy load this is not possible, so that it isthen necessary to switch over to an operating mode using externallyapplied (spark) ignition, in particular to a homogeneouslystoichiometric mode of operation. The switchover between said operatingmodes is performed taking into account variables such as fuelconsumption, exhaust emissions and drivability as a function ofcorresponding operating parameters such as, for example, load and enginespeed.

During the operation of the internal combustion engine, however,exceptional situations can arise in which this customary “switchoverstrategy” leads to a disadvantageous mode of operation.

SUMMARY OF THE INVENTION

The object of the present invention is to specify a method forcontrolling the operation of an HCCI internal combustion engine of sucha kind wherein the setting of the operating mode suitable for saidexceptional situation is ensured even in exceptional situations.

This object is achieved by the method defined in the claims.

The present invention is based on the knowledge that in certainexceptional situations during the operation of the internal combustionengine the HCCI operating mode must be either prevented or enforced inorder to avoid the malfunctions and damage contingent on the exceptionalsituation.

According to an alternative it is provided according to the inventionthat operation of the internal combustion engine in the HCCI operatingmode is prevented if at least one of the following events occurs:

-   -   a) the vacuum in a vacuum reservoir of an associated braking        system is less than a limit value due to an excessively high        pressure in the intake duct of the internal combustion engine;    -   b) the scavenge rate of a fuel tank venting valve of an        associated fuel tank venting system of the internal combustion        engine is less than a limit value due to an excessively high        pressure in the intake duct of the internal combustion engine;    -   c) the temperature of the coolant of a cooling circuit of the        internal combustion engine is less than a minimum value;    -   d) the measurement of the air mass and/or the pressure in the        intake duct of the internal combustion engine is defective;    -   e) the ignition of the air-fuel mixture and/or the fuel        injection is defective;    -   f) ignition failures (misfires) or extremely uneven running of        the internal combustion engine occur;    -   g) a safety device for monitoring the control functions of the        internal combustion engine detects a system error.

If the internal combustion engine is in the HCCI operating mode when oneof the events a) to g) occurs, it is switched to an operating mode usingexternally applied (spark) ignition, for example to a homogeneouslystoichiometric or homogeneous lean mode of operation. If the internalcombustion engine is already in an operating state using externallyapplied (spark) ignition when one of the events a) to g) occurs, aswitchover to the HCCI operating mode is prevented.

According to the second alternative it is provided according to theinvention that operation of the internal combustion engine in the HCCIoperating mode is enforced if at least one of the following eventsoccurs:

-   -   a) the recirculation rate of an exhaust gas recirculation system        of the internal combustion engine is greater than a limit value        as a result of a malfunction;    -   b) the air-fuel ratio (λ) is less than 1 in spite of the fuel        injection being switched off.

By means of the measures according to the invention it is possible toprevent malfunctions of and damage to the internal combustion engine aswell as dangerous states occurring in the event of the specifiedexceptional situations.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details of the method according to the invention will beexplained with reference to the drawings, in which:

FIG. 1 shows a schematic representation of an HCCI internal combustionengine;

FIG. 2 is a flowchart of a method for preventing an HCCI mode ofoperation in certain exceptional situations;

FIG. 3 is a flowchart of a method for enforcing an HCCI mode ofoperation in certain exceptional situations.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows in a highly schematized form a spark ignition type internalcombustion engine 1 of the piston design type having at least onecylinder, an intake duct 2, an exhaust gas duct 3, an intake valve, anexhaust valve, an ignition device 4, a fuel injection valve 5, and athrottle valve 6. Arranged in the intake duct 2 are sensors 7, 8 forsensing the air mass or, as the case may be, the pressure in the intakeduct. A sensor 9 in the form of a lambda probe is disposed in theexhaust gas duct 3 in order to sense the air-fuel ratio (λ).

Assigned to the internal combustion engine 1 is an electronic operationcontrol device 10 which receives measurement signals from the sensor 7to 9 as well as further sensors (not shown) and outputs actuatingsignals to the ignition device 4, the fuel injection valve 5, and thethrottle valve 6 as well as further actuators of the internal combustionengine.

Certain other components of the internal combustion engine which arerelevant to the present invention are also indicated schematically inFIG. 1, specifically an exhaust gas recirculation system 11 having anexhaust gas recirculation valve 12, a braking system 16 having a vacuumreservoir 17, and a pressure sensor 18 for sensing the vacuum in thevacuum reservoir 17, as well as a fuel tank venting system 13 having afuel tank venting valve 14 and an activated charcoal reservoir 15.

The internal combustion engine 1 is embodied as an HCCI internalcombustion engine which is normally operated in the HCCI operating modeunder the control of the electronic operation control device 10 and isswitched over to a mode of operation using externally applied (spark)ignition in certain operating states (e.g. high engine speed or heavyload) as a function of specific operating parameters (e.g. engine speedand load). Since such methods for controlling the operation of theinternal combustion engine 1 are known (e.g. from the publications citedat the beginning), they will not be explored in further detail here.

Irrespective of the operating states occurring during normal operationof the internal combustion engine, however, exceptional situations canoccur which would lead to a serious malfunction if no intervention ismade by means of the method according to the invention.

Thus, for example, there are exceptional situations in which operationof the internal combustion engine 1 in the HCCI operating mode can leadto malfunctions and serious damage. The method according to theinvention, which will now be explained in more detail with reference tothe flow diagram of FIG. 2, prevents an HCCI operating mode if at leastone of the following exceptional situations occurs:

-   -   a) Low vacuum in the vacuum reservoir 17: The HCCI operating        mode requires a relatively high pressure in the intake duct 2,        i.e. the throttle valve 6 is wide open essentially independently        of the driver's wishes (pedal position). Under certain operating        conditions this can lead to a state in which the vacuum        reservoir 17 connected to the intake duct 2 in order to provide        braking support to the braking system 16 can no longer be        adequately vented.

Thus, if the vacuum in the vacuum reservoir 17 sensed by means of thepressure sensor 18 is less than a predefined limit value (step 25), thehomogeneously stoichiometric operating mode is set (step 33).

If the vacuum in the vacuum reservoir 17 is greater than the limitvalue, then the program goes on to the next step 26.

b) Tank ventilation: The high pressure in the intake duct 2 that is setin the HCCI operating mode can further lead to the scavenge rate of thefuel tank venting valve 14 becoming so low that the fuel tank (notshown) is no longer adequately vented. Since the scavenge rate of thefuel tank venting valve 14 is continuously monitored in any case bymeans of a model by the electronic operation control device 10, thescavenge rate can be compared with a limit value. If the scavenge rateis less than the limit value (step 26), a transition is made to thehomogeneously stoichiometric or even to the homogeneously lean mode ofoperation (step 33).

Otherwise the program proceeds to step 27.

c) Vehicle interior heating: In the HCCI operating mode a substantialimprovement in the efficiency of the internal combustion engine isproduced in certain operating ranges. There is then no longer so muchwaste heat available for heating the coolant of the cooling system 19.At low outside temperatures this then causes the coolant to heat up onlyrelatively slowly, thus adversely affecting the operation of the vehicleinterior heating system accordingly. Consequently, if the temperature ofthe coolant measured by means of the temperature sensor 20 does notincrease to a minimum value (step 27), a switch is made to thehomogeneously stoichiometric mode of operation (step 33).

Otherwise the program continues to step 28.

d) Sensor error: If the air sensing by means of the air mass sensor 7and/or the pressure sensor 8 in the intake duct 2 is defective, atorque-neutral switchover between the HCCI mode and an operating modeusing externally applied (spark) ignition is no longer possible. Inorder, namely, to avoid a torque surge in a switchover of this type,precise values must be available for the air mass flow or, as the casemay be, the pressure in the intake duct 2.

Thus, if the air sensing is defective (step 28), the internal combustionengine will be operated in the homogeneously stoichiometric operatingmode. Toward that end it is first determined whether the internalcombustion engine is currently in the HCCI operating mode (step 32). Ifthis is the case, a switch is made to the homogeneous stoichiometricoperating mode (step 33). If the internal combustion engine is alreadyin an operating mode using externally applied (spark) ignition, theswitchover to the HCCI operating mode is prevented (step 34).

e) Faulty ignition or fuel injection: If the ignition (ignition device4) and/or the fuel injection (injection valve 5) are malfunctioning,that is to say if the corresponding actual values of the ignition and/orinjection cannot be brought into line with the predefined set values, atorque-neutral switchover between the HCCI operating mode and anoperating mode using externally applied (spark) ignition is likewise nolonger possible or at least is made considerably more difficult. In thiscase too, therefore, the homogeneously stoichiometric operating modewill be activated exclusively (steps 29 and 32 to 34).

f) Ignition failures (misfires) and extremely uneven running: Theelectronic operation control device 10 typically includes a device 21for detecting misfires and/or for monitoring the even running of theinternal combustion engine. If, for example, misfires or extremelyuneven running occur in certain engine speed or load ranges,problem-free operation in the HCCI mode is also no longer guaranteed insaid operating ranges. In these cases too, therefore, the HCCI operatingmode should be avoided, at least in said engine speed or load ranges(steps 30 and 32 to 34).

g) Safety concept: The electronic operation control device is typicallyprovided with a safety device 22 for monitoring the control functions ofthe internal combustion engine (safety concept). If the monitoring ofthe HCCI operating mode no longer works correctly due to a system error,the HCCI operating mode must be avoided. Otherwise reliable operation ofthe internal combustion engine would no longer be guaranteed. There isthe risk, for example, that because of the throttle valve 6 being wideopen in the HCCI operating mode an unintended acceleration of thevehicle will occur if, for example, in the HCCI operating mode, asdetected by a reasonableness check, the exhaust gas recirculation rateor the injected fuel quantity is not reasonable and the ignitioncontinues to be operated. Thus, if the safety device 22 detects a systemerror (step 31), the HCCI operating mode is prevented from the outset(step 34).

With the operations described above, either a switchover from the HCCIoperating mode to an operating mode using externally applied (spark)ignition was enforced or a switchover to the HCCI operating modeprevented. On the other hand there are exceptional situations in whichthe HCCI operating mode should be set, which operating mode is thenenforced according to the invention. This will now be explained withreference to the flowchart shown in FIG. 3.

-   -   a) External exhaust gas recirculation system: If an        unintentionally high exhaust gas recirculation rate is produced,        for example as a result of an exhaust gas recirculation valve 12        sticking in the open position or a fault in the control of the        exhaust gas recirculation valve 12, a controlled operation using        externally applied (spark) ignition, in particular a        homogeneously stoichiometric operation, is no longer possible        because the combustion process becomes unstable. Thus, if the        exhaust gas recirculation rate is greater than a limit value        (step 35), it is established as a first step whether the        internal combustion engine is currently in the HCCI operating        mode (step 38). If this is the case, a transition to an        operating mode using externally applied (spark) ignition is        prevented (step 39). If, on the other hand, the internal        combustion engine is in an operating mode using externally        applied (spark) ignition, in particular in the homogeneous        stoichiometric mode of operation, a switch is made to the HCCI        operating mode (step 40).

If, on the other hand, the exhaust gas recirculation rate is less thanthe limit value, the program proceeds to step 36.

b) Fuel tank ventilation: If the fuel tank venting valve 14 sticks inthe open position and the pressure in the intake duct 2 (under lightload) is low, the inducted fuel vapors can result in an air-fuel ratiowhich is less than 1 in spite of the fuel injection being switched off.If this is the case (steps 36 and 37), then the internal combustionengine will be operated in the HCCI mode (steps 38 to 40), assuming thisis not already the case anyway.

1. A method for controlling the operation of an HCCI internal combustion engine, comprising: operating the internal combustion engine in the HCCI operating mode or in an operating mode using externally applied (spark) ignition and during normal operation in a predefined switchover method is switched between the operating modes as a function of predefined operating parameters, wherein irrespective of the predefined switchover method, operation of the internal combustion engine in the HCCI operating mode is prevented if at least one of the following exceptional situations occurs; the vacuum in a vacuum reservoir of an associated braking system is less than a limit value due to an excessively high pressure in the intake duct of the internal combustion engine; the scavenge rate of a fuel tank venting valve of an associated fuel tank venting system of the internal combustion engine is less than a limit value; the temperature of the coolant of a cooling circuit of the internal combustion engine is less than a minimum value; the measurement of the air mass and/or the pressure in the intake duct of the internal combustion engine is defective; the ignition of the air-fuel mixture and/or the fuel injection is defective; misfires or extremely uneven running of the internal combustion engine occur; and a safety device for monitoring the control functions of the internal combustion engine detects a system error.
 2. The method as claimed in claim 1, wherein if the internal combustion engine is being operated in the HCCI operating mode and at least one of the events as claimed in claim 1 occurs, the internal combustion engine will be switched over to an operating mode using externally applied (spark) ignition.
 3. A method for controlling the operation of an HCCI internal combustion engine, comprising: operating the internal combustion engine in the HCCI operating mode or in an operating mode using externally applied (spark) ignition and during normal operation in a predefined switchover method is switched between said operating modes as a function of predefined operating parameters, characterized in that, irrespective of the predefined switchover method, operation of the internal combustion engine in the HCCI operating mode is enforced if at least one of the following exceptional situations occurs; the recirculation rate of an external exhaust gas recirculation system of the internal combustion engine is greater than a limit value as a result of a malfunction; and the air-fuel ratio is less than 1 in spite of the fuel injection being switched off. 